# classmates = ['Michael', 'Bob', 'Tracy']
# print(classmates)

# print(len(classmates))
# print(classmates[0])
# print(classmates[-3])

# classmates.append('Adam')
# print(classmates)

# classmates.insert(1, 'Jack')
# print(classmates)

# classmates.pop(2)
# print(classmates)

# classmates[2] = 'Sarah'
# print(classmates)

# k = ['asp', 'j']
# s = ['python', 'java', k, 'scheme']
# print(s[2][1])

# L = ['Adam', 'Lisa', 'Bart', ['Jack', 'Rose']]
# print(len(L))

# t = ('a', 'b', ['A', 'B'])
# t[2][0] = 'X'
# t[2][1] = 'Y'
# print(t)

L = [
    ['Apple', 'Google', 'Microsoft'], 
    ['Java', 'Python', 'Ruby', 'PHP'], 
    ['Adam', 'Bart', 'Bob']
    ]

# 打印Apple:
print(L[0][0])
# 打印Python:
print(L[1][1])
# 打印Bob:
print(L[2][2])